CHAPTER XIV 
BACTERIA AND OTHER MICROORGANISMS IN 
CHEESE 
CHEESE-RIPENING 
Cheese consists primarily of the casein and fat of milk, collected 
first as a curd and then allowed to undergo a series of chemical 
changes called ripening. Ordinarily the casein is precipitated 
from the milk by rennet, although it is done in sonie types of 
cheese by simple souring. Then the curd is separated more or 
less from the whey, and pressed into definite shape. The whey 
removes most of the milk-sugar, and the cheese retains about 
two-thirds of the food material in the milk, and since it is in a 
very dense form, it is one of the most nutritious of our foods. 
The popularity of cheese as a food depends rather upon its flavor 
than its food value and the flavor develops during the ripening. 
Cheese-ripening is a very complex phenomenon and one as yet 
only partly understood. This is due partly to the intricacy of 
the subject and partly also to the fact that there are very many 
different kinds of cheeses, and the ripening of the different types 
is not by any means the same. Although there are some hundred 
varieties of cheese, they may be arranged fairly well into two 
groups: (1) The hard cheeses, and (2) the soft cheeses. The 
ripening of the hard cheeses is very different from that of the 
soft, and the ripening of the different types of soft cheese varies 
greatly one from the other. Each kind of cheese must, therefore, 
be studied as a special problem. 
Chemical and Physical Changes.—During the ripening, 
the cheese, which is at first rather hard, tough and elastic, gradu- 
ally becomes softer. The extent of this softening depends largely 
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